In virtue of the integrative function of the general principle of good faith, there are duties that must be assumed by the parts, even if they have not committed to it expressly, such as the duties of disclosure, loyalty, confidentiality, coherence and collaboration, among others. The present paper intends to determine the juridical nature of civic responsibility derived from the failure to comply with such duties, bearing in mind the different positions presented by comparative law and by national doctrine and jurisprudence. The study takes into account the phases of the contact and the practical and conceptual difficulties present in each of them.